Forced magnetic reconnection, caused by a prominence from the Sun, was seen for the first time in images from NASA’s Solar Dynamics Observatory, or SDO. This image shows the Sun on May 3, 2012, with the inset showing a close-up of the reconnection event imaged by SDO’s Atmospheric Imaging Assembly instrument, where the signature X-shape is visible. Credit: NASA/SDO/Abhishek Srivastava/IIT(BHU).
NASA’s Solar Dynamics Observatory has observed a magnetic explosion
the likes of which have never been seen before. In the scorching upper
reaches of the Sun’s atmosphere, a prominence — a large loop of material
launched by an eruption on the solar surface — started falling back to
the surface of the Sun. But before it could make it, the prominence ran
into a snarl of magnetic field lines, sparking a magnetic explosion.
Scientists have previously seen the explosive snap and realignment of
tangled magnetic field lines on the Sun — a process known as magnetic
reconnection — but never one that had been triggered by a nearby
eruption. The observation, which confirms a decade-old theory, may help
scientists understand a key mystery about the Sun’s atmosphere, better
predict space weather, and may also lead to breakthroughs in the
controlled fusion and lab plasma experiments.
“This was the first observation of an external driver of magnetic
reconnection,” said Abhishek Srivastava, solar scientist at Indian
Institute of Technology (BHU), in Varanasi, India. “This could be very
useful for understanding other systems. For example, Earth’s and
planetary magnetospheres, other magnetized plasma sources, including
experiments at laboratory scales where plasma is highly diffusive and
very hard to control.”
Previously a type of magnetic reconnection known as spontaneous
reconnection has been seen, both on the Sun and around Earth. But this
new explosion-driven type — called forced reconnection — had never been
seen directly, thought it was first theorized 15 years ago. The new
observations have just been published in the Astrophysical Journal.
The previously-observed spontaneous reconnection requires a region
with just the right conditions — such as having a thin sheet of ionized
gas, or plasma, that only weakly conducts electric current — in order to
occur. The new type, forced reconnection, can happen in a wider range
of places, such as in plasma that has even lower resistance to
conducting an electric current. However, it can only occur if there is
some type of eruption to trigger it. The eruption squeezes the plasma
and magnetic fields, causing them to reconnect.
While the Sun’s jumble of magnetic field lines are invisible, they
nonetheless affect the material around them — a soup of ultra-hot
charged particles known as plasma. The scientists were able to study
this plasma using observations from NASA’s Solar Dynamics Observatory, or SDO, looking specifically at a wavelength of light showing particles heated 1-2 million kelvins (1.8-3.6 million F).
The observations allowed them to directly see the forced reconnection
event for the first time in the solar corona — the Sun’s uppermost
atmospheric layer. In a series of images taken over an hour, a
prominence in the corona could be seen falling back into the
photosphere. En route, the prominence ran into a snarl of magnetic field
lines, causing them to reconnect in a distinct X shape.
Forced magnetic reconnection, caused by a prominence from the Sun, was seen for the first time in images from NASA’s SDO.
Credits: NASA's Goddard Space Flight Center.
Download this video in HD formats from NASA Goddard's Scientific Visualization Studio
Spontaneous reconnection offers one explanation for how hot the solar atmosphere is — mysteriously, the corona is millions of degrees hotter than lower atmospheric layers, a conundrum that has led solar scientists for decades to search for what mechanism is driving that heat. The scientists looked at multiple ultraviolet wavelengths to calculate the temperature of the plasma during and following the reconnection event. The data showed that the prominence, which was fairly cool relative to the blistering corona, gained heat after the event. This suggests forced reconnection might be one way the corona is heated locally. Spontaneous reconnection also can heat plasma, but forced reconnection seems to be a much more effective heater — raising the temperature of the plasma quicker, higher, and in a more controlled manner.
While a prominence was the driver behind this reconnection event, other solar eruptions like flares and coronal mass ejections, could also cause forced reconnection. Since these eruptions drive space weather — the bursts of solar radiation that can damage satellites around Earth — understanding forced reconnection can help modelers better predict when disruptive high-energy charged particles might come speeding at Earth.
Understanding how magnetic reconnection can be forced in a controlled way may also help plasma physicists reproduce reconnection in the lab. This is ultimately useful in the field of laboratory plasma to control and stabilize them.
The scientists are continuing to look for more forced reconnection events. With more observations they can begin to understand the mechanics behind the reconnection and often it might happen.
“Our thought is that forced reconnection is everywhere,” Srivastava said. “But we have to continue to observe it, to quantify it, if we want prove that.”
Spontaneous reconnection offers one explanation for how hot the solar atmosphere is — mysteriously, the corona is millions of degrees hotter than lower atmospheric layers, a conundrum that has led solar scientists for decades to search for what mechanism is driving that heat. The scientists looked at multiple ultraviolet wavelengths to calculate the temperature of the plasma during and following the reconnection event. The data showed that the prominence, which was fairly cool relative to the blistering corona, gained heat after the event. This suggests forced reconnection might be one way the corona is heated locally. Spontaneous reconnection also can heat plasma, but forced reconnection seems to be a much more effective heater — raising the temperature of the plasma quicker, higher, and in a more controlled manner.
While a prominence was the driver behind this reconnection event, other solar eruptions like flares and coronal mass ejections, could also cause forced reconnection. Since these eruptions drive space weather — the bursts of solar radiation that can damage satellites around Earth — understanding forced reconnection can help modelers better predict when disruptive high-energy charged particles might come speeding at Earth.
Understanding how magnetic reconnection can be forced in a controlled way may also help plasma physicists reproduce reconnection in the lab. This is ultimately useful in the field of laboratory plasma to control and stabilize them.
The scientists are continuing to look for more forced reconnection events. With more observations they can begin to understand the mechanics behind the reconnection and often it might happen.
“Our thought is that forced reconnection is everywhere,” Srivastava said. “But we have to continue to observe it, to quantify it, if we want prove that.”
Source: NASA/SDO Solar Mission
Related Links
- The Heart of Space Weather Observed in Action
- NASA Spacecraft Discovers New Magnetic Process in Turbulent Space
- NASA Keeps Watch Over Space Explosions
- Learn more about SDO
By Mara Johnson-Groh
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Editor: Rob Garner
